Supib Report post Posted October 19, 2010 The question goes as follows: In a certain town three newspapers are published. 20% of the population read A, 16% read B, 14% read C, 8& read A and B, 5% read A and C, 4% read B and C, and 2% read all 3. A person is selected at random. Use a venn diagram to help determine the probability that the person reads:a.) none of the papers b.) at least one of the papers c.) exactly one of the papers d.) either A or B e.) A given that the person reads at least 1 paper f.) C, given that the person reads either A or B or both. Now I've tried to solve this problem for about an hour now, cant seem to even get the correct answer for a... answers are: a.) 13/20 b.) 7/20 c.) 11/50 d.) 7/25 e.) 4/7 f.) 1/4gah got my november math sl retakes in 2 weeks and I'm stuck on this... I regret not taking math studies, but oh well if anyone does help thank you ! Share this post Link to post Share on other sites

genepeer Report post Posted October 19, 2010 (edited) To reduce the confusion of percentages, let's assume the town (universal set) has 100 people.That means the circle for A=20 people, B=16 people, and C=14 people.We will then skip ahead and see "2% read all". That means 2 people are at AnBnC (center).Now 8 people read A and B, and we know 2 read all. Then 6 people read A and B but not C.5 people read A and C, and we know 2 read all. Then 3 read A and C but not B.Similarly, 2 read B and C but not A.The remaining numbers in circles are filled in such that, all the numbers in A add up to 20, B up to 16, and C up to 14.The universal set is 100 but the sum of all number in circles is 35. Therefore there's 65 outside.I just did a venn diagram to illustrate what I just described.a) The number outside the circles represent the number of people who don't read. Therefore Probability = 65/100 = 13/20b) The total number inside circles = 35, this is the number of people who read at least one newspaper (A, B, or C). Probability = 35/100 = 7/20c) Sum of numbers in no intersection = 9+6+7 = 22, number of people who read just one (hence not being in intersection). Probability = 22/100 = 11/50d) It's better to say A or B. Adding 'Either' implies (A or B but not both) which isn't what was meant here judging from the answer. Sum of all number in A or B, 9+3+6+2+6+2=28, number of people reading A or B. Probability = 28/100 = 7/25e) Number of people reading A = 20 (given in question) and 35 read at least one newspaper (from part b.) Probability = 20/35 = 4/7f) Again it would have been better to just say 'A or B' instead of adding 'either' and having to avoid confusion by adding 'or both'. 'Either A or B or both' is the same as just 'A or B'. Anyway, number of people reading A or B = 28 (from d.), and of these, sum of numbers in C too = 3+2+2 = 7, number of people reading C given that they read A or B. Probability = 7/28 = 1/4.Sorry, can't give better explanation through text; ask someone to explain it to you in person if you still don't understand. Edited October 19, 2010 by Gene-Peer 1 Share this post Link to post Share on other sites

Supib Report post Posted October 20, 2010 you have no idea how grateful I am ! thank and nah I understand now, I see what I did wrong. I didnt subtract the amount of people who read all newspapers from the amount of people who read A and B and B and C. Share this post Link to post Share on other sites

dessskris Report post Posted October 20, 2010 Automatic generated messageThis topic has been closed by a moderator.Reason: question answeredIf you disagree with this action, please report this post, and a moderator or administrator will review it.Kind regards,IB Survival Staff Share this post Link to post Share on other sites